The present invention relates to a method for manufacturing magnet armatures.
German Patent Application DE 19730276 A1 [hereinafter referred to as E1] teaches that it is advantageous to provide the magnet armature of a solenoid valve with a plastic coating, for reasons of dimensional stability and sliding properties thereof. FIG. 2 therein describes a 3/2-way valve, in other words a valve with two valve seats, representing the maximum possible number of valve seats in the embodiment with only one magnet armature.
On the valve closure face [(3) therein] of the armature [(1) therein] there is provided a coating which prevents damage to the face when this strikes the valve seat [(4) therein] upon actuation of the magnet.
When the magnet actuation is turned off, the second closure face [(19) therein] is caused by the action of the restoring spring to strike the second valve seat [(20) therein], whereby it is further advantageous to provide a coating on the second valve closure face as well for protection against damage. Furthermore, the faces [(6) therein] of the armature in contact with the guide device [(5) therein] are provided with a coating to increase sliding capability.
Finally, it is proposed that the entire armature be provided with a coating in one working cycle, for example by immersion. This very cost-effective total coating of the magnet armature is possible for the valve types presented therein, but all valve seats shown therein are designed as metal-to-metal sealing seats, which do not have a hermetic seal.
In the case of application in pilot units for brake-pressure modulators of electronically controlled brake systems in vehicles, there are usually provided in each channel at least three pilot valves [“air admission”, “venting”, redundant pressure function], which are designed as solenoid valves but which must have a hermetically sealing valve seat in their closed position, to ensure that the pressure in the control chamber of the downstream relay valve is maintained when the pilot valves are not actuated. The function and principle of action of such pilot solenoid valves is described in German Patent Application 10009117.2, which does not represent a prior disclosure, and which is referred to hereinafter as E2.
FIG. 4 of E2 illustrates the valve types with which such pilot units can be constructed: They comprise a 2/2-way valve which is closed when the energizing current is off [(43) and (44) in FIG. 4 therein], a 2/2-way valve which is open when the energizing current is off [(45) and (46) in FIG. 4 therein] and a 3/2-way valve [(47) and (48) in FIG. 4 therein].
For each of the cited valve types there is shown in FIG. 4 therein the magnet armature [(39) therein], which is provided at one end with a molding [(42) therein] for formation of a metal-to-metal sealing seat that is not hermetically sealing, and at the other end with an elastomeric insert [(41) therein] for formation of the hermetically sealing valve seat.
The magnet armatures according to FIG. 4 of E2 cannot, however, be equipped with a total coating such as proposed in E1.
The reason for this is that the elastomeric inserts according to FIG. 4 of E2 are vulcanization-bonded into corresponding cavities of the magnet armatures, and so an adhesive elastomer-to-metal bond exists between the ferromagnetic base material of the magnet armature and the elastomeric insert.
This metal-to-elastomer bond is produced with the help of an adhesion promoter which acts between the base metal and the elastomer in the manner explained hereinafter. Because the adhesion promoter has extremely sensitive functional ability, however, it is effective only if a well prepared metal surface is present, as explained hereinafter; the use of such a thin plastic coating between the base metal and the elastomeric insert rules out any secure adhesion of this insert. For this reason a plastic coating of the cavity for the elastomeric insert is not possible, whereby total coating of the magnet armature for such pilot solenoid valves is ruled out.
The foregoing explanations about FIG. 4 of E2 are familiar as such to those skilled in the art; E2, which is not a prior disclosure, is mentioned here merely because FIG. 4 therein illustrates the common types of pilot valves all together.
Accordingly, it is desired to provide a method for manufacturing magnet armatures, while overcoming the disadvantages associated with prior art methods and magnetic armatures.